1. Field of the Invention
The present invention relates to a transmission method of digital data typified by DVD-Video and others, and particularly to a transmission method of stream data or a command outputted from a stream data sending device, and a command or flow control information outputted from a stream data receiving device.
2. Description of the Related Art
There is a conventional method for transmitting data recorded on a CD (compact disk) or the like, called MOST (Media-Oriented Synchronous Transfer), for example. (References: Patric Heck, et al.: “Media Oriented Synchronous Transfer—A Network Protocol for High-Quality, Low-Cost transfer of Synchronous, Asynchronous, and Control Data on Fiber Optic”, Presented at AES103rd Convention, 1997 September, Preprint 4551, or www.rnostcooperation.com)
The conventional data transmission method according to the MOST method will be explained below with reference to FIG. 1.
FIG. 1 is a diagram that shows a data structure of a frame in the MOST method.
According to the conventional transmission method, data is transmitted in a frame transmitted at 44.1 kHz, that is, every 22.67 microseconds. A data length of one frame is 512 bits. As shown in FIG. 1, one frame consists of a preamble 701, a boundary descriptor 702, a synchronous channel area 703, an asynchronous channel area 704, a control frame 705, a frame control data 706 and a parity 707. The frame cycle is not limited to 44.1 kHz, but may be 48 kHz. In the following explanation, the frame cycle is 44.1 kHz, for convenience.
Here, the preamble 701, the boundary descriptor 702, the synchronous channel area 703 in the frame will be explained, but the explanation of the asynchronous channel area 704, the control frame 705, the frame control data 706 and the parity 707 will be omitted because they are not directly related to the present invention.
The preamble 701 is data of 4 bits having a fixed pattern, and used for detecting a boundary of a frame in a sending device and a receiving device that transmit the data. The boundary descriptor 702 is data of 4 bits and is used for indicating the boundary between the synchronous channel area 703 and the asynchronous channel area 704.
The synchronous channel area 703 is data of 0˜480 bits long, and its length is determined by the boundary descriptor 702. The synchronous channel area 703 is used for transmission of real time data such as voice data. Here, the real time data means the data with time constraints, and in transmission of that data, the transmission delay must be definable.
The synchronous channel area 703 is assigned to the sending device and the receiving device as a time slot. Up to 60 time slots can be used as a synchronous channel. The time slots used for transmission are assigned to the sending device and the receiving device in advance, and a group of time slots used for one transmission is defined as a logical channel. The sending device sends data using the assigned time slot, and the receiving device receives the data using the assigned time slot. In the MOST method, data transmission using one time slot corresponds to the data transmission at a speed of 352.8 kbps. In other words, five time slots are used in the synchronous channel area 703 in order to transmit data of a CD at a speed of 1.6122 Mbps.
A command or the response thereto is usually transmitted using the control frame 705.
In the conventional transmission method, the stream data is transmitted using the synchronous channel area 703, and the command is transmitted using the control frame 705. As for DVD (digital versatile disk)-Video, the disk includes compressed data under the standard of MPEG-2. Since the speed of reading out data by the drive device is generally higher than that of decoding the data by the decoding unit, flow control occurs in the drive device. Therefore, when the data of DVD-Video is transmitted via a network, the information on this flow control (hereinafter referred to as “flow control information”) also needs to be transmitted.
However, the method for transmitting the flow control information is not determined in the MOST method, so the above flow control cannot be executed appropriately.